Provide a way to exempt a terminal from applying any env collections

[karrtikr]

We can provide:

• a terminal filter function to decide which terminals environment collection applies to
• an option to skip env collection in terminal startup options

Primary use case:

With #145234 coming up, we would like to shift some commands which we run as a process to running in terminal instead, but we would like to run those in a deactivated terminal (similar to process spawn), instead of the one where envs are already set.

[karrtikr]

It was brought to my attention that environment collection isn't applied on hidden terminals:

vscode/src/vs/workbench/contrib/terminal/browser/terminalProcessManager.ts

Lines 438 to 441 in 443f8cc

	if (!this._isDisposed && !shellLaunchConfig.strictEnv && !shellLaunchConfig.hideFromUser) {
	this._extEnvironmentVariableCollection = this._environmentVariableService.mergedCollection;
	this._register(this._environmentVariableService.onDidChangeCollections(newCollection => this._onEnvironmentVariableCollectionChange(newCollection)));

Which means they're deactivated already, so we can directly use them to run commands, i.e this feature should no longer be needed.

[Tyriar]

@karrtikr we could change it as it makes sense to me that hideFromUser would behave the same.

[karrtikr]

Umm I kind of like it because hidden terminals are generally extension specific (for eg. microsoft/vscode-remote-release#1760), so it does not care for environment collection of other extensions.

(Also, it allows us to workaround this issue 😉)

[karrtikr]

Reopening this issue as it would seem that we're also deciding to apply environment collection to hidden terminals: #197187 (comment).

[Tyriar]

Closing as hidden terminals will act like regular terminals with #199611 (comment).